1. Field of the Invention
This invention relates generally to MacPherson strut type suspension using a strut consisting of a shock absorber and a coil spring, and more particularly to a strut mount insulator through which the strut is mounted on a vehicle body.
2. Description of the Prior Art
Strut type suspensions are in general so arranged that at one end of the strut a shock absorber cylinder is mounted to move with the vehicle wheel, and at the other end of the strut the shock absorber piston rod is connected to the vehicle body, thereby suspending the vehicle body, engine and power train above the wheels. The strut is installed to the vehicle body through an insulator mainly including an insulator rubber in order to prevent the vibration from the wheels from being transmitted to the vehicle body.
A coil spring of the strut is usually disposed between an upper spring seat secured to a strut outer cylinder and a lower spring seat supported through the insulator rubber on the vehicle body, so that the spring action of the coil spring is effected between the strut outer cylinder and the piston rod. Accordingly, the coil spring is secured at its upper end to the vehicle body through the upper spring seat and the insulator rubber, and therefore a high unsprung weight is applied to the insulator rubber. As a result, in the case where the elastic modulus of the insulator rubber is relatively low, the insulator rubber unavoidably deforms to an appreciable extent under a relatively strong external force due to the extension and contraction of the coil spring which supports the vehicle body weight, i.e., due to the vertical movement of the wheels. This not only requires a large space for the moving stroke of the suspension but also lowers the strength of the insulator rubber, thereby degrading the durability thereof. On the contrary, if the elastic modulus of the insulator rubber is increased, the insulator rubber cannot effectively absorb the high frequency vibration which is transmitted thereto from the wheels through the shock absorber piston rod to the vehicle body, which high frequency vibration is mainly due to so-called stick phenomena or stationary relationship between the piston rod and the cylinder of the shock absorber. Such high frequency vibration is transmitted to the vehicle body, thus emitting noise. In this regard, the thus arranged conventional suspension cannot meet the above-mentioned conflicting requirements, and consequently the elastic modulus of the insulator rubber is set unavoidable at a compromise value, taking the above conflicting requirements into consideration.
In view of the above, it is the object of this invention to overcome the above-discussed drawbacks encountered in the conventional strut type suspension.